Thermoelectric junction for an indirectly heated cathode



D. VlTZTHUM 3,385,997

THERMOELECTRIC JUNCTION FOR AN INDIRECTLY HEATED CATHODE May 28, 1968 Filed June 22, 1966 INVENTOR fl//fier Wfz/fium BY J M ATTYS.

United States Patent 6 Claims. ((51. 315-55) ABSTRACT OF THE DISCLOSURE An indirectly heated cathode having a thermoelectric junction formed by a cathode body of one metal and a cathode support of a second metal, individual lead-out lines .for the cathode body and the cathode support of the same metal as the cathode body and the cathode sup port, respectively.

The invention relates to an indirectly heated cathode, with at least one thermoelectric junction, for electrical discharge vessels, and is of special importance in high power tubes.

In sealed electron tubes, it is generally impossible to determine the cathode temperature because appropriate windows for a pyrometric measuring are missing, occasioned by the fact that in the overwhelming number of cases, such windows cannot even be provided. There are no other possibilities for temperature measurement, particularly without interruption ofthe emission process. It is, however, often necessary to determine the cathode temperature, especially in order to effect a correction thereof. This may, for example, be the case when the cooling of the tube involved is replaced, or when the operating point is altered, for example, by increased cooling of the emission plans due to increased electron emission.

An incandescent cathode with an electron emitting layer and a direct current heater for semi-indirect heating is already known, the heating element of which, heated by direct current, may possess one or several thermoelectric junctions which, as so-called hot places, have good heat transition relations with respect to the cathode body and which serve for the increase of the heat economy by means of the appearing Peltier effect. Since that p rtion of the heat effective through the Peltier effect, is below one percent for a present low heating voltage of 2 volts, this known arrangement has, due to the required very low heating voltage, no practical importance.

It is, therefore, the purpose of the invention, by a special construction, for example by a relatively simple change or supplement to an indirectly heated cathode, especially of an MK-cathode, to make the momentary actual cathode temperature during the emission process available in such a way that its value may serve for a monitoring, and most important of all, for the control of temperature regulation.

According to the invention, this is achieved, in an indirectly heated cathode as initially described by the feature that the cathode body, consisting of a customarily used metal, such as molybdenum, nickel or the like, is employed as the one metal conductor, and is fastened, in particular welded, to a cathode support, consisting of such a different metal as platinum, tantalum or the like, which functions as the second metal conductor, so that a thermoelectrical junction is created, with the electrical connections to the parts constituting the two metal conductors being led separately out of the discharge vessel and the respective lead Wires thereof, up to a cold point, in particular up to the exist point, consisting of the same metal as the associated metal conductor.

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An especially advantageous development of the invention is obtained in the case of a disk cathode if the radiation protective shell is produced from a tantalum foil cylinder and used as one of the metal conductors as it enters directly up to the emission plane formed by the emission carrier disk. The use of molybdenum and tantalum as the metals for the two hollow conductors has, 'with respect to the thermoelectric junction, the important advantage that, in the range or lower temperatures, the characteristic course is very fiat so that, for example, at a surrounding temperature in the range of 15 to 30 C., the deviation per degree centigrade amounts, at most, to one third percent. Naturally, other metal conductor combinations with molybdenum or nickel as: the most common metals for cathode carriers are likewise possible.

Additional details of the invention will be explained in connection with an MK-cathode, purely schematically illustrated in the drawing, as an example of a construction of a storage cathode. Such parts not directly contributing to an understanding of the invention, have been emitted or are not designated.

In a cathode, for example, as used in a beam production system of a frequency modulation tube, the cathode body 1, not illustrated in detail, primarily comprises a storage container and a space for the heater involved, which may be either a free-standing or a cemented heater. At its upper edge, directly below the porous emission material carrier disk 2, a molybdenum ring 3 is rigidly connected to the cathode body, for example by sintering. The radiation protective shell 4, for example, made of a tantalum foil cylinder, can be welded to the molybdenum ring in such a way that such attachment forms a thermoelectric junction 5. Because of the immediate nearness of such junction with respect to the emission plane, the temperature there prevailing corresponds quite exactly to the actual emission temperature. The respective electrical connections, at least up to a sufliciently cold spot, in particular to the exit point thereof from the tube, comprise, for the tantalum foil cylinder, a tantalum wire 6, and for the cathode body, a molybdenum Wire 7. Both metal conductors forming lead wires 6 and 7 are segregated from other corresponding systems, and are separately led out of the discharge vessel. The thermovoltage produced at the thermoelectric junction 5, may be obtained at the respective lead conductors and measured to determined the emission temperature, as well as utilize for the control of temperature regulation means to which the heating current is responsive.

In the event the emission current is simultaneously conducted over one of such leads, the voltage drop appearing at the respective metal conductor, for example at the foil cylinder, lying in series with the thermovoltage, must be compensated.

In an MK-cathode with a frontal emission plane of 3 mm. diameter, at an operating temperature of 1085 C., the cooling of the emission plane, caused directly by the emission process, was found to be 0.28:0.03 C./ma. Accordingly, for an emission of ma.corresponding to a specific emission of 1.4 A./ per cm. the result would already be a possibly important cooling of approximately 28 C.

Within the scope of the invention, a particularly advantageous arrangement for thermoelectric control of the temperature of an indirectly heated cathode may be produced in which the electric voltage, taken at the two metal conductors, and separately conducted, is applied to a temperature regulator which operates according to a compensation method, in which the deviation from the desired temperature value serves as a control voltage. In this case, the deviation of the thermocontrol voltage may, according to the particular requirements and the permissible expenditure, be accomplished with or without a short interruption of the emission process. By such a method, it is possible, without difiiculty, even with a change in the operation of the cathode, to regulate the emission temperature by an appropriate temperature regulator to within approximately one-half degree accuracy.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An indirectly heated cathode, with at least one thermoelectric junction, for electric discharge vessels, comprising a cathode body, consisting of a customary metal such as molybdenum, nickel or the like, forming one metal conductor, a cathode support, consisting of a different metal, such as platinum, tantalum or the like, forming the second metal conductor to which the cathode body is attached, particularly Welded, forming a thermoelectric junction, the parts forming the two metal conductors having individual lead-out lines to the exterior of the discharge vessel, such lead lines, up to a cold spot, in particular up to the lead-out point, consisting respectively of the same metal as the associated metal conductor.

.2. An indirectly heated cathode according to claim 1, wherein the cathode is a disk cathode, a radiation protective shell comprising a tantalum foil cylinder and forming one of the metal conductors of the thermoelectric junction.

3. An indirectly heated cathode according to claim 1, wherein said cathode is an MK-cathode, particularly for tubes of high power, and having a storage container, covered by a porous, emission material carrier disk, consisting of molybdenum, and forms one of the metal conductors of the thermoelectric junction.

4. An indirectly heated cathode according to claim 1, wherein the parts forming the two metal conductors are connected by means of respective lead lines with a thermoelectric temperature measuring device.

5. An indirectly heated cathode according to claim 1, wherein the parts forming the two metal conductors are connected by means of respective lead lines with a temperature regulation device.

6. An indirectly heated cathode according to claim 1, wherein at the separately led-out metal conductors of the thermoelectric junction, formed by parts of the cathode, the electric voltage, produced during operation, is conducted to a temperature regulator controlling the heating current, said regulator operating, in particular, in the manner of a compensation circuit.

References Cited UNITED STATES PATENTS 2,146,365 2/1939 Batchlor 3l338 2,416,565 2/1947 Beggs 313-38 X 2,655,614 10/1953 Doolittle et al 313-38 X 2,677,787 5/1954 Litton 315-55 JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

